Wow... those are really low chances.
Last year I crossed one of my ZS X F1's with a semi-determinate black F2, and expected the odds to be 1/2 sp/sp and 1/2 black. But only one in 4 would have a single Beta allele. I grew 4 plants this year, got 2 black, no Beta, and 0/4 sp/sp - all indeterminates. Now I understand that the sp from ZS is segregating only with the Beta allele...
who knew.
Very helpful information, thank you all.